Non-local diffusion and the chemical structure of molecular clouds

We present an application of a non-local turbulent transport model (currently being used to model transport in magnetically confined laboratory plasmas) to the study of the chemical structure of a molecular cloud. We consider a 'toy model' chemistry with a single molecular species which is adsorbed/desorbed from grain surfaces. With this idealized chemistry, we are able to find analytic solutions to both the 'classical' turbulent diffusion model as well as to the non-local transport model. For the turbulent diffusion model, we find that for the turbulent transport to be important one needs a mixing length comparable to the size of the cloud. On the other hand, with the non-local transport model we find that the chemistry is already strongly affected by the turbulent transport for mixing lengths two orders of magnitude smaller than the cloud size. This model then has the desirable property of being able to mix material over long distances (compared with the size of a molecular cloud) without requiring an inordinately large characteristic size for the turbulent eddies.